Studies completed, underway, or planned include investigations of the role of in vivo metabolism, distribution and tissue macromolecular binding of MeCCNU, in mediating the nephrotoxicity of MeCCNU in Fischer 344 rats. Ongoing studies are designed to explore the effects of drug metabolism inducers and inhibitors, as well as the effect of depletion of tissue glutathione levels on the covalent binding, disposition and toxicity of MeCCNU. Preliminary experiments have also addressed the role of the carbamoylating and alkylating activity of MeCCNU in relation to this compound's nephrotoxicity. Initial studies were conducted in Fischer rats administered MeCCNU labeled either within the carbamoylating [(cyclohexyl-1-14C)-MeCCNU] or alkylating [(2-chloroethyl-1,2-14C)-MeCCNU] region of the compound. These studies show fat to accumulate the highest tissue levels (nmoles/g wet weight) of parent compound (determined by HPLC analysis of tissue extracts). Kidney accumulated the highest tissue levels of the more polar ether and methanol extractable metabolites and/or degradative products of MeCCNU. Moreover, carbamoylation of tissue protein by (cyclohexyl-1-14C)-MeCCNU and alkylation of DNA by (2-chloroethyl-1,2-14C)-MeCCNU were higher in kidney than in any other tissue. Thus, as yet, no clear-cut case can be made for either carbamoylation or aklylation for MeCCNU-induced nephropathy. Further studies are needed to examine the metabolism, distribution and covalent binding of chloroethyl-1,2-14C- and cyclohexyl-1-14C MeCCNU in animals given treatments known to alter the nephrotoxicity of MeCCNU. In previous studies, we found that compounds known to induce (3-methylcholanthrene) or inhibit (piperonyl butoxide) drug metabolism provided some protective effect on the nephrotoxicity of MeCCNU. Moreover, a compound that decreased tissue glutathione levels (buthionine sulfoximine) also enhanced the nephrotoxicity of MeCCNU. Studies are now underway in which the distribution and binding of MeCCNU will be conducted in animals that have been pretreated with the aforementioned agents. The overall goals of these studies are to characterize the biochemical mechanisms underlying the nephrotoxicity of MeCCNU.